Overview
This lecture covers the life cycle of ferns, the first type of vascular plants, focusing on how they reproduce via spores and comparing their life cycle with that of mosses.
Ferns as Seedless Vascular Plants
- Ferns are seedless vascular plants, unlike most vascular plants which use seeds.
- Mosses are nonvascular and ferns are vascular, marking a major evolutionary difference.
Fern Life Cycle Steps
- Life cycle begins with fertilization: haploid sperm and egg form a diploid zygote.
- Fertilization occurs in the archegonium, the female part of the plant.
- Zygote grows into an embryo, which becomes the diploid sporophyte.
- The mature sporophyte is the dominant, photosynthetic generation in ferns.
- Underneath fronds are sori (singular: sorus), clusters of sporangia.
- Sporangia produce haploid spores via meiosis.
- Released spores develop into a young gametophyte, the haploid generation.
Gametophyte Details
- Fern gametophytes are hermaphroditic (monoecious), containing both male (antheridia) and female (archegonium) organs.
- Antheridia produce sperm; archegonium produces eggs.
- Water is needed for sperm to swim from antheridia to archegonium for fertilization.
- After fertilization, a new zygote is formed, restarting the cycle.
Ferns vs. Mosses Life Cycles
- Ferns have a dominant sporophyte (diploid) generation; mosses have a dominant gametophyte (haploid) generation.
- Both ferns and mosses depend on water for fertilization and reproduce by spores, not seeds.
- Nomenclature for reproductive structures (archegonium and antheridia) is the same in both groups.
Key Terms & Definitions
- Sporophyte — Diploid, multicellular stage that produces spores.
- Gametophyte — Haploid, multicellular stage that produces gametes.
- Archegonium — Female reproductive structure producing eggs.
- Antheridium — Male reproductive structure producing sperm.
- Sorus (pl. sori) — Cluster of sporangia on fern fronds.
- Sporangium (pl. sporangia) — Structure where spores are formed.
- Monoecious (Hermaphroditic) — One organism with both male and female reproductive organs.
- Alternation of generations — Plant life cycle alternating between haploid gametophyte and diploid sporophyte stages.
Action Items / Next Steps
- Review the diagram of the fern life cycle.
- Compare the life cycles of ferns and mosses for similarities and differences.